In a conventional semiconductor process, a photolithographic process is usually used to form traces over a chip or a substrate. However, this process is technically limited in the processing of features having a line width smaller than 100 nanometers due to the light diffraction. Therefore, a nanoimprint lithographic (NIL) process is proposed to replace the photolithographic process for manufacturing devices with very high resolution, with a high throughput and a low manufacturing cost.
FIG. 6A through to FIG. 6C illustrate the operation of a nanoimprint lithographic including a cycle of heating, imprinting, and cooling. At the heat stage as shown in FIG. 6A, a moldable layer applied over a substrate 31 is heated to an operating temperature required for imprinting. In FIG. 6B, a mold 22 having nanoscale features 23 is mounted on an upper molding plate 20′, and the mold 22 is driven by a power source 50 to move toward the substrate 31 mounted on a lower molding plate 30′. When the mold 22 comes into contact with a moldable layer 32 which is formed above the substrate 31, the mold 22 is pressed against the moldable layer 32 to make an engagement, so that the features on the mold 22 are transferred to the moldable layer 32. The moldable layer 32 is then cooled down to a proper temperature. In FIG. 6C, the moldable layer 32 is disengaged from the mold 22 to complete the nanoimprint lithographic process.
Since the nanoimprint process is carried out at the level of nanoscale, the imprinting process is certainly tighter in terms of quality control than the conventional hot embossing process. However, as can be understood from the operation process described previously, the mold 22 and the nanoscale features 23 may be deformed or distorted, resulting uneven imprint depths as shown in FIG. 7A if the pressure is not uniformly applied during the nanoimprint process. Referring to FIG. 7B, the mold 22 may not be parallel to the substrate 31, as the nanoscale features 23 are tilted above the area to be imprinted, causing deterioration in the imprint quality. The situations described above may cause damage to the nanoscale features 23 during the demolding stage. Therefore, molding quality and manufacture efficiency in mass production are both degraded due to non-uniform distribution of imprinting pressure and poor parallelism between the mold and the substrate. These problems often occurred as a result of poor designs or inferior processing/assembly of the imprint equipment, and apparently need to be resolved by improving the imprinting equipment
FIG. 8 is a schematic view of a hot embossing apparatus disclosed in U.S. Pat. No. 5,993,189. An imprint mold 63 and a substrate 64 are respectively carried on an inner carrier 61 and an outer carrier 62, which carriers are in relative movement. A power source then drives the carriers 61, 62 to engage, so that the nanoscale features of the imprint mold 63 are pressed against the moldable layer which is formed above the substrate 64. As this apparatus is not provided with any parallelism adjustment, a desired parallelism is achieved solely via processing or assembly of its parts. And with such apparatus design, there are too many modifications in terms of processing and assembly of the parts, making it difficult to satisfy the nanoimprinting requirements, as well as to manufacture equipment of the same quality by mass production. Furthermore, since the conventional force transmission mechanism does not satisfy the requirement of uniform pressure distribution in the nanoimprint lithographic process, it is not easy to maintain imprint quality.
FIG. 9 illustrates a fluid pressure imprint lithography apparatus disclosed in U.S. Pat. No. 6,482,742. After a mold 72 and a substrate 73 coated with a moldable layer are sealed, they are placed in a closed chamber 74 and heated to a predetermined molding temperature. The chamber 74 is then filled with fluid to exert pressure on the mold 72, so as to perform nanoimprinting. According to this apparatus design, the mold 73 and substrate 73 are stacked and encapsulated into a seal before imprinting, and the seal has to be broken after the pattern is transferred to allow demolding. Accordingly, the stacking and sealing of the mold 72 and the substrate 73 increase both the processing costs and molding period, resulting in inefficient nanoimprinting. And since the mold 72 and substrate 73 need to be sealed before the imprinting, it is also difficult to perform alignment for the mold 72 and the substrate 73. As a result, the imprint quality and precision are degraded.
FIG. 10 illustrates a nanoscale imprint lithography apparatus disclosed in PCT Patent No WO 0142858. The apparatus is formed with a pressure chamber 82 that can be pressurized via an inlet channel 83. With pressure exerted by fluid, a mold 81 is pushed toward or away from a substrate 85 as a result of deformation of a flexible membrane 84, so as to complete nanoimprinting or demolding. But if the mold 81 is not placed at center of the flexible membrane 84, the flexible membrane 84 may expand asymmetrically when the inlet channel 83 is filled with fluid, thereby causing the mold 81 to misalign from the substrate 85.
Therefore, the above-mentioned problems associated with the prior arts are resolved by providing a uniform pressing apparatus applicable to nanoimprinting to improve the nanoimprint quality, while the apparatus has benefits in terms of excellent parallelism, simple structure, low cost, simple operation procedures, and fast molding.